It is known to couple a power take-off (PTO) to an engine of a vehicle to allow the internal combustion engine of the vehicle to provide rotational motion and torque to auxiliary components. For example, if a hydraulic pump is coupled to a PTO, the hydraulic pump can be used to provide hydraulic fluid to an electrical generator or other hydraulic equipment. Oftentimes, hydraulic pumps are coupled to vehicles that have four-wheel drive. In this configuration, a forward driveshaft reduces clearance near the PTO where a pump may be mounted.
A variety of solutions have been attempted to overcome the lack of space or clearance proximate a PTO due to the presence of a forward driveshaft in a four-wheel drive vehicle. One solution is to use a smaller pump that fits within the space constraints dictated by the presence of the forward driveshaft. However, in certain applications it is desirable to employ a pump that is larger than the space available due to the presence of the forward driveshaft. For example, a variable displacement pump is typically larger than a gear pump. When a hydraulic circuit is supplied by a variable displacement pump, a load sense line that is fluidly coupled to the variable displacement pump causes adjustment of the flow delivered by the pump in order to maintain a constant pressure drop across an orifice disposed in the hydraulic circuit. In this manner, variable input provided by the PTO due to fluctuations in revolutions per minute (RPM) of an engine that is not idling, are compensated for by the variable displacement pump and constant hydraulic fluid flow is provided to a hydraulic motor/generator despite fluctuations in vehicle RPM. Thus, by using a variable displacement pump, a generator may be operated to power certain life saving equipment in emergency vehicles while the vehicle is being driven.
A second solution is to employ a gearbox provided by Muncie Power Products, Inc. of Muncie, Ind. to allow a driveshaft to extend from the gearbox rearward of the vehicle and beyond the transfer case where there are less space constraints for mounting a hydraulic pump. The Muncie gearbox employs three gears, which results in a speed increase and less torque than if the pump were coupled directly to the PTO without the Muncie gearbox being coupled therebetween. Moreover, a universal joint is often coupled to the driveshaft rearward beyond the transfer case to allow the pump to be positioned higher, so as not to reduce the drive clearance of the vehicle.
A third solution to the problem of lack of space near a forward driveshaft is to extend a shaft from the power take off through the transfer case where there are less space constraints to negotiate in mounting a hydraulic pump. U.S. Patent Application Publication No. 2013/0213157 filed on Feb. 16, 2012 to Martin et al., the disclosure of which is hereby incorporated by reference, discloses a transfer case including a passage way through which a PTO shaft is received. The drawbacks of this solution are the time and labor required to modify the transfer case to allow a driveshaft to extend through it.
A need exists to adapt a variable displacement pump to a four-wheel drive vehicle in a manner that provides clearance from a forward driveshaft without the drawbacks described above.